What’s happened to acid rain?

Dear Control Engineering: How come we never read about acid rain in our newspapers anymore? Not even in Minnesota, land of 10,000 tree huggers. Tom D., retired control engineer.

As the graph from the U.S. EPA shows, acid rain reductions are a success story in that the amount has indeed declined for a number of reasons. Most relate to coal use, as sulfur content is the primary source. Here are a few specifics:

EPA regulations have worked in that they have driven utilities to install scrubbers and other remediation strategies. The Economist pointed out that 53% of coal-fired generating capacity now has scrubbers.

Coal-fired generation is declining overall. Ten years ago, coal-fired plants accounted for 52% of our electricity. Now that figure is 45%, and predictions suggest that downward trend will continue as natural gas and renewables grow.

As the Economist article notes, there are many more costs related to producing and burning coal than most people realize. There are technologies to mitigate the problems, but these are generally only installed at newer facilities. Getting over the problems will take time, but you may have more trees to hug.